Is this addressed to me? I have to admit I am being disagreeable with some people's opinions in non-personal matter, but I haven't realised I have insulted someone by doing that.
My apologies if that's how it came across
Air Stones....
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Is this addressed to me? I have to admit I am being disagreeable with some people's opinions in non-personal matter, but I haven't realised I have insulted someone by doing that.
My apologies if that's how it came across
Try that on my small 7 gallon tank, I would have to throw the fish out to do so.
I think whether you use an air pump or power head additionally, or more powerful filter just depends on the size of tank,current setup, personal preference and requirements of the tank. I certainly don't need anything else in my small tank, as the filter is circulating the water about 17 times an hour(400L/H) and the outflow is a long srpay bar splashing this into the surface, but with a less powerful filter which most tanks come with, I don't see this being the case.
this does not make sense. 5x or 25x the same proportion of water will be moved in any size tank. so the flow will no be higher in a smaller tank..
as for the thread subject. the science is clear. though you seem to resist it.
The power head in the 7 gallon tank is as big as one of the filter power heads in the 30 gallon tank. The small tank has a spray bar all along the back of the surface which agitates all the surface and is quite strong. The filters in my 30 gallon do not come with a spray bar, one is a hood filter, the other is Fluval U4 and they don't do too much at the surface to be honest, maybe from one side mostly. Probably with a different filter outflow, it could be a different story. At the moment I can't rearrange the current filters to get better movement at the top, so hence the air bubbler.
As for the science, I must be reading a different science than you do obviously. It just seems that it doesn't suit your opinion, and you prefer to turn this into a personal insult, to distract from the main subject.
as for science. bignose has provided it. it seems to be you, who will not accept the facts. as yet you have provided not evedence that the science, from bignose, is in any way incorrect. so my conclusion is inescapable.
as for flow. you seem to be confusing flow with water speed.
flow, to a large extent is dictated by the filters pump power. and, unless you have a way of increasing or decreasing the pumps output, is fixed.
water speed can be increased, or decreased, simply by adjusting the size of the output venturi. and will not affect the water flow in any, significant, way..
the U4? it would seem most people, with this filter, dont have your problems. which is interesting!
i go back to my original point. you have a problem in your tank. I suggest you find its real cause. or at least, consider other causes. if it were down to an airstone, we would all need to use them. and we dont!
I may be confusing flow and speed, but you tend to think these are unrelated and the amount of water the filter outputs if positioned at the surface does not impact the speed at which the surface moves?
And I am also wrong to think, that an air pump does not contribute to the movement of the water at all?
No matter how much you disturb the surface of the water with the best filter output pipe in the world, it won't get oxygenated, unless something moves the saturated water away from the surface and distrubutes it at the lower levels, whether this depends on how the filter output is positioned, is another question.
So what's your point? I never denied that the bubbles from the air pump itself are not the way the water gets the oxygen, but you are telling me that the oxygen knows whether the water surface is being moved by the filter output pipe or by an air pump?
As for the output of my U4, it can be setup to ouput the water at the bottom of the tank, or the middle, so if set this way, instead of the surface output, then I'd have no water surface movement at all and I would need something else to do that job. So as I said, it depends on personal setup, it's not an absolute rule that your filter will provide enough oxygen, depending on the filter and the way it is setup in a tank.
This isn't right. Diffusion of the oxygen will always tend from higher to lower until equilibrium is reached. Perfectly still water that starts devoid of oxygen will reach equilibrium oxygen levels in just a matter of time. It is a function of how deep the still water goes. But, since the surface is exposed to an unlimited source of oxygen, and diffusion will always take oxygen from high levels to low, it will be completely oxygenated.
The circulation of the water does increase this mixing significantly, several orders of magnitude. But, the mixing is not necessary.
Mikaila31
Always Watching
I just really hate bubbles. They aren't natural at all.... and they are noisy >.>
But that's the point. The surface of the water gets oxygenated even if completely still, but it doesn't get exposed to "unlimited amount of oxygen" as you say. The oxygenation stops once the oxygen level at the surface and air have reached equilibrium/reached same oxygen concentration levels? Therefore you need something to move that surface water away, by the means of an filter pump spraybar, etc..., hence the statement about needing water surface movement in a tank. If the diffusion law worked so well in the average not so deep fish tank, and oxygen from the surface did get diffused itself to the lower levels, then we need no filter outflow tube, or watever surface movement in this case?
On another note, if there is more oxygen concentration levels in the water than in the air(like in nature when plants produce additional oxygen), then disturbing the water will start the process of degassing, which depletes the oxygen from the water.
the biggest problem with your argument is, the glaring errors in logic you display.
you say you "may" confuse flow and water speed. but if you dont understand that connection. none of your conclusions can be taken seriously. simply because you , clearly, dont fully understand what's going on.
or, possibly more correctly, you misconceptions stop you fully understanding it.
and its not water sped that circulates the tank. its water flow. as a result, the surface water will make one trip from outlet to inlet for each tank cycle.
so a tank with 5x flow will change the surface water, at least, 5 times an hour.
which, logically, is the same speed there rest of the tanks water cycles at!
anyway, we are getting nowhere.
you wont accept the PROPER science that is offered.
we cant accept your flawed thinking.
so, I will leave it at that.
but be aware, each time you proffer your view
it will be countered in much the same way, as it was here.
with proper, fully understood, science.
OK, I understand your point, but we are talking about oxygenating, not circulating water. What if your inlet is positioned at the bottom and your outlet is positioned at the bottom? This water may not be oxygenated yet and mixing it this way may not contribute too much to the oxygenation(as it can be set on a U4 filter for example). Bignose said that diffusion normally happens from top to bottom, not the other way round, so even if the oxygenated water is flown at the middle or bottom of the tank, then is the oxygen going to diffuse the other way round too? If yes, then you don't need surface movement.
If the oxygenation happens at the surface only, as Bignose stated, then turbulence of water at the surface does depend on all factors that contribute to that, filter outlet, air pump, power head etc..
If I don't understand, then explain my stupid questions, rather than laughing at them.
It is unlimited. Do you know how large the atmosphere is? If you filled the entire space of the water with pure oxygen taken from the atmosphere, how much have you lowered the concentration in the atmosphere? 0.0000000000001%? For all purposes, zero, hence you can treat the atmosphere as a source of infinite oxygen.
If you really want to learn about this, you need to study the stagnant diffusion problem.
It looks like this: A----------------------B where the space between A & B is initially completely devoid of substance Z (call it oxygen if you want). At time t=0, a valve at A is open, and substance Z is allowed to diffuse into the space between A and B. The solution to this is: Concentration of Z as a function of time t = A1 + A2*erf( ((x-xb)/(xa-ab))/sqrt(4*D*t)) A1 & A2 are constants based on the boundary conditions. D is the diffusion rate. and erf is the Error Function: http
/en.wikipedia.org/wiki/Error_function The graph on the wikipedia page is good, because it is just like the solution at hand. Imagine the left hand side as A, and the right hand side as B. The front of the substance Z is the red line. At time goes on, it spreads out and moves to the right. Eventually it will fill the entire space A to B, it is only a matter of time with an infinite source available.And this is what will happen with oxygen and water. It is only a matter of time -- eventually all the water will reach maximum oxygen saturation, with no flow. This is how diffusion works. A substance will always diffuse from high to low concentrations.
Again, mixing this will speed the process up 10 fold at least. Mixing is good. But, it will eventually saturate without mixing. That is the nature of diffusion with infinite sources. I hope this doesn't sound like I'm being a jerk, but this is mass transfer 101. These are homework problems that all students in a mass transfer class do. This is phenomena that is really well understood for many, many years now.
If you want sources for some good mass transfer texts that do through the details of this problem, just ask and I can provide them.
I didn't say that oxygen in the atmosphere is limited exactly.
The reason I said that limited amount of oxygen from the unlimited source of oxygen in the atmosphere will enter the water, is because oxygen dissolves in water by diffusion laws as you said,but only until the saturation level(dissolved oxygen in water) has reached 100%.
Theoretically, after saturation levels have reached 100% and more percent, the opposite process of degassing happens, when oxygen leaves the water and goes into the atmposphere.
It looks like this: A----------------------B where the space between A & B is initially completely devoid of substance Z (call it oxygen if you want). At time t=0, a valve at A is open, and substance Z is allowed to diffuse into the space between A and B. The solution to this is: Concentration of Z as a function of time t = A1 + A2*erf( ((x-xb)/(xa-ab))/sqrt(4*D*t)) A1 & A2 are constants based on the boundary conditions. D is the diffusion rate. and erf is the Error Function: http
And this is what will happen with oxygen and water. It is only a matter of time -- eventually all the water will reach maximum oxygen saturation, with no flow. This is how diffusion works. A substance will always diffuse from high to low concentrations.
I don't think that diffusion of oxygen in water and diffusion of oxygen in air will give you exactly the same results. But here is what I found from an article about the diffusion law you are talking about:
"Oxygen is absorbed in water by direct diffusion and by surface-water agitation. Solubility of oxygen in water is so small and by diffusion process alone in still water, it was calculated that it would take 6 years for oxygen to diffuse from surface to a depth of 6 meters in quiet water.
The low diffusion of oxygen in water referred to already and the stratification of gases even in small bodies of water, unlike atmospheric air which is uniform, make each water body distinct in its nature."
(http
/www.fao.org/docrep/field/003/AC183E/AC183E04.htm)
Lufbramatt
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After some thinking, and taking on board the fact that airstones may be a usefula safety backup, I installed an airstone (with non return valve to protect the pump) on a timer switch that turns teh bubbles on while I am asleep or at work, then turns them off in the evening when I am likely to be in the same room as the tank. So I can see if theres a problem, but cant see or hear the air pump.
Right, but there is a limitless source of oxygen available to reach saturation. That means that you can treat the source as infinite, and you get equations that describe a diffusion front that will eventually reach 100% saturation everywhere. It doesn't matter what the specific saturation or diffusion numbers are... an infinite source means that everything will evenutally reach 100%. And this started by your claiming that diffusion alone can't do that, which is wrong. Diffusion very much can and does.
Regarding the second point there, nature always tends toward equilibirum. The only way water would achieve a level greater than 100% saturation is if conditions change -- such as the water warms up quickly. Given constant conditions, nature won't overshoot equilbirum and then have to come back down. Outgassing would only occur if conditions significantly changed from a previous state.
Then you would think wrong. Because the laws of diffusion do not change depending on the medium it is diffusing through. Diffusion through a gas, liquid, or a solid are identical. Now, the specific diffusion rates will be different, but the laws remain identical, and hence the mathematical forms of the solution remain identical.
Oxygen diffusion through nitrogen (in effect air) has a diffusion rate of around 0.250 cm[sup]2[/sup]/s
Oxygen diffusion through water has a diffusion rate around 0.000025 cm[sup]2[/sup]/s.
About 4 orders of magnitude difference (the specific values will be a function of temperature, in both cases), as is typical when comparing diffusion rates in liquids and gases.
But here is what I found from an article about the diffusion law you are talking about:
"Oxygen is absorbed in water by direct diffusion and by surface-water agitation. Solubility of oxygen in water is so small and by diffusion process alone in still water, it was calculated that it would take 6 years for oxygen to diffuse from surface to a depth of 6 meters in quiet water.
The low diffusion of oxygen in water referred to already and the stratification of gases even in small bodies of water, unlike atmospheric air which is uniform, make each water body distinct in its nature."
(http
I am not sure that 6 years is completely accurate. It really is doing to depend on a lot of factors. Nonetheless, the bigger point is that diffusion alone CAN saturate the water. It will take time.
A bigger point is that this has strayed quite some ways from seeking an answer for some of the original questions. No fish tank is completely quiescent. They all have mixing from filter returns and even the fish swimming in them provide significant mixing. What started this was a question whether bubbles or the tank surface provides more gas in a typical fish tank.
You can't compare the case of diffusion from only bubbles AND use the mixing bubbles provide to the case of a completely still tank with diffusion only from the surface. You need to compare actual use cases; or in other words, you need to compare apples to apples, instead of apples to orangutans. If you want to compare diffusion through the surface of a still tank with diffusion through 250 bubbles somehow suspended in a still tank, then the top of the tank will provide orders of magnitude more oxygen because of the greater surface area. Or, if you want to compare the mixing caused by the filter return and the diffusion from the top of the tank to the mixing causes by rising bubbles and the diffusion out of those bubbles, the top of the tank will once again be much greater.
In any situations that are comparable, the top of the tank provides a much greater surface area than any reasonable amount of bubbles. It is simply that greater area that shows that the vast, vast majority of the gas mass transfer that occurs comes from the top.
Lufbramatt
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ok, if we look at a real world example, life in the african rift valley lakes is limited to the upper reaches of the water as there is not enough oxygen to support life (the deeper water is anoxic). There is no real current to move the water around, only diffusion to distribute dissolved gases. These lakes have been there for millions of years yet diffusion has not completely oxygenated the water?
If you want an actual case study about this, check out the Black sea. It is a meromictic lake, meaning upper and lower layers of the water do not mix. Diffusion alone has not helped for at least several thousand years so there is no oxygen there below 200m. How long do you think it will take for the diffusion law to work it's charm in the Black sea as it's bottom is completely depleted of oxygen.
The below is from a quick wiki search, but I can find something better if you insist:
The Black Sea is the world’s largest meromictic basin where the deep waters do not mix with the upper layers of water that receive oxygen from the atmosphere. As a result, over 90% of the deeper Black Sea volume is anoxic water.
P.S. I have never claimed that a certain number of bubbles will oxygenate the water. You came up with formulas and bubble numbers where all I was trying to say is that regardless of whether bubbles dissolve in water or not, the bubbles do hit the surface causing water surface movement and thus helping in oxygenating the water. You were the one to argue several times that it is the water surface movement that oxygenates the water. Now you are argueing that diffusion alone without water mixing will still reach all levels. Yes, I agree, but how many thousands of years will that take? It certainly hasn't happened in the Black Sea yet.
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